By default Visual Studio will always perform build of every project in your solutuion when you run a single project. Even if that project doesn’t depend on every other project in your solution.
Go to Tools | Options | Projects and Solutions | Build and Run and check the box “Only build startup projects and dependencies on Run“.
Since now when run your project (F5 key), Visual Studio will only build your startup project and the those projects in your solution that it depends on.